SQSTM1/p62 deficiency induces oxidative stress and senescence in vivo and in vitro in VSMCs

Aging is a major contributor to age-related diseases including cardiovascular disease (CVD). Vascular senescence, a hallmark of mammalian aging, has been linked to vascular disease like atherosclerosis. We previously showed that the NADPH oxidase Nox1 mediates senescence induced by angiotensin II, a major inducer of vascular aging and CVD. Disruption of other processes, like autophagy, also promotes senescence due to the accumulation of dysfunctional mitochondria leading to upregulation of ROS levels. SQSTM1, known as p62, is an autophagy adaptor involved in the targeting of protein aggregates and dysfunctional organelles, including mitochondria, into the autophagy degradation pathway. The interaction between NADPH oxidases and autophagy in the senescence pathway is incompletely understood. Using vascular smooth muscle cells (VSMCs) isolated from aortas of p62 +/+ and p62 -/- mice, we found that lack of p62 causes senescence by a ROS-dependent and Nox1-independent mechanism. Downregulation of p62 decreased cell proliferation, increased the expression of the senescence markers (senescence associated-β-galactosidase (SA-β-gal) and p21) and increased superoxide, hydrogen peroxide and mitochondrial ROS levels. Treatment with the antioxidant N-acetyl cysteine (NAC) and the mitochondrial ROS scavenger MitoTEMPO reduced SA-β-gal activity in p62 -/- VSMCs, suggesting that cytosolic ROS, as well as mitochondrial ROS contribute to the development of senescence. These effects were not associated with upregulation of Nox1. Further, senescence was also upregulated in vivo in aortas of male and female p62 -/- , compared with p62 +/+ mice. Altogether, these data suggest lack of p62 induces oxidative stress by a Nox1-independent and mitochondrial-dependent mechanisms.